Added '-timing' commandline argument, which determines the type of waiting

to do between processing frames, and can be set to 'sleep' or 'busy'.
Sleep emulates previous Stella behaviour, releasing the CPU whenever
possible (at the expense of graphical tearing on some systems, unless
gl_vsync is enabled).  Busy emulates the busy-wait behaviour of z26,
using all available CPU time but sometimes eliminating (or at least
reducing) graphical tearing.


git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@1526 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba

stella/Changes.txt

@@ -30,6 +30,12 @@
     calculation.  Also, re-enabled changing the framerate from within the
     UI.
 
+  * Added '-timing' commandline argument, which sets the type of waiting
+    between processing frames.  Setting it to 'sleep' emulates the
+    previous behaviour in Stella; setting it to 'busy' emulates z26,
+    and can in some cases eliminate screen tearing (at the expense of
+    using all available CPU time).
+
   * Fixed issue with debugger disassembly and mirrored $40 TIA write
     addresses.  They were actually defined at $30, and generating incorrect
     labels.

stella/docs/index.html

@@ -240,6 +240,12 @@
     calculation.  Also, re-enabled changing the framerate from within the
     UI.</li>
 
+<li>Added '-timing' commandline argument, which sets the type of waiting
+    between processing frames.  Setting it to 'sleep' emulates the
+    previous behaviour in Stella; setting it to 'busy' emulates z26,
+    and can in some cases eliminate screen tearing (at the expense of
+    using all available CPU time).</li>
+
 <li>Fixed issue with debugger disassembly and mirrored $40 TIA write
     addresses.  They were actually defined at $30, and generating incorrect
     labels.</li>
@@ -657,6 +663,16 @@
 			<td>Enable/disable the PAL color-loss effect.</td>
 		</tr>
 
+		<tr>
+			<td><pre>-timing &lt;sleep|busy&gt;</pre></td>
+			<td>Determines type of wait to perform between processing frames.
+				Sleep will release the CPU as much as possible, and is the
+				preferred method on laptops (and other low-powered devices)
+				and when using GL VSync.  Busy will emulate z26 busy-wait
+				behaviour, and use all possible CPU time, but may eliminate
+				graphical 'tearing'.</td>
+		</tr>
+
 		<tr>
 			<td><pre>-framerate &lt;number&gt;</pre></td>
 			<td>Display the given number of frames per second.  Normally, Stella

stella/src/emucore/OSystem.cxx

@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: OSystem.cxx,v 1.128 2008-05-21 14:50:41 stephena Exp $
+// $Id: OSystem.cxx,v 1.129 2008-05-21 16:49:07 stephena Exp $
 //============================================================================
 
 #include <cassert>
@@ -797,20 +797,42 @@ void OSystem::stateChanged(EventHandler::State state)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void OSystem::mainLoop()
 {
-  for(;;)
+  if(mySettings->getString("timing") == "sleep")
   {
-    myTimingInfo.start = getTicks();
-    myEventHandler->poll(myTimingInfo.start);
-    if(myQuitLoop) break;  // Exit if the user wants to quit
-    myFrameBuffer->update();
-    myTimingInfo.current = getTicks();
-    myTimingInfo.virt += myTimePerFrame;
+    // Sleep-based wait: good for CPU, bad for graphical sync
+    for(;;)
+    {
+      myTimingInfo.start = getTicks();
+      myEventHandler->poll(myTimingInfo.start);
+      if(myQuitLoop) break;  // Exit if the user wants to quit
+      myFrameBuffer->update();
+      myTimingInfo.current = getTicks();
+      myTimingInfo.virt += myTimePerFrame;
 
-    if(myTimingInfo.current < myTimingInfo.virt)
-      SDL_Delay((myTimingInfo.virt - myTimingInfo.current) / 1000);
+      if(myTimingInfo.current < myTimingInfo.virt)
+        SDL_Delay((myTimingInfo.virt - myTimingInfo.current) / 1000);
 
-    myTimingInfo.totalTime += (getTicks() - myTimingInfo.start);
-    myTimingInfo.totalFrames++;
+      myTimingInfo.totalTime += (getTicks() - myTimingInfo.start);
+      myTimingInfo.totalFrames++;
+    }
+  }
+  else
+  {
+    // Busy-wait: bad for CPU, good for graphical sync
+    for(;;)
+    {
+      myTimingInfo.start = getTicks();
+      myEventHandler->poll(myTimingInfo.start);
+      if(myQuitLoop) break;  // Exit if the user wants to quit
+      myFrameBuffer->update();
+      myTimingInfo.virt += myTimePerFrame;
+
+      while(getTicks() < myTimingInfo.virt)
+        ;  // busy-wait
+
+      myTimingInfo.totalTime += (getTicks() - myTimingInfo.start);
+      myTimingInfo.totalFrames++;
+    }
   }
 }
 

stella/src/emucore/Settings.cxx

@@ -13,7 +13,7 @@
 // See the file "license" for information on usage and redistribution of
 // this file, and for a DISCLAIMER OF ALL WARRANTIES.
 //
-// $Id: Settings.cxx,v 1.146 2008-05-21 14:01:30 stephena Exp $
+// $Id: Settings.cxx,v 1.147 2008-05-21 16:49:07 stephena Exp $
 //============================================================================
 
 #include <cassert>
@@ -55,6 +55,7 @@ Settings::Settings(OSystem* osystem)
   setInternal("grabmouse", "false");
   setInternal("palette", "standard");
   setInternal("colorloss", "false");
+  setInternal("timing", "sleep");
 
   // Sound options
   setInternal("sound", "true");
@@ -214,6 +215,10 @@ void Settings::validate()
   if(s != "soft" && s != "gl")
     setInternal("video", "soft");
 
+  s = getString("timing");
+  if(s != "sleep" && s != "busy")
+    setInternal("timing", "sleep");
+
 #ifdef DISPLAY_OPENGL
   s = getString("gl_filter");
   if(s != "linear" && s != "nearest")
@@ -308,6 +313,7 @@ void Settings::usage()
     << "                 user>\n"
     << "  -colorloss    <1|0>          Enable PAL color-loss effect\n"
     << "  -framerate    <number>       Display the given number of frames per second (0 to auto-calculate)\n"
+    << "  -timing       <sleep|busy>   Use the given type of wait between frames\n"
     << endl
   #ifdef SOUND_SUPPORT
     << "  -sound        <1|0>          Enable sound generation\n"